Bibcode
Ponti, G.; Bianchi, S.; Muñoz-Darias, T.; Mori, K.; De, K.; Rau, A.; De Marco, B.; Hailey, C.; Tomsick, J.; Madsen, K. K.; Clavel, M.; Rahoui, F.; Lal, D. V.; Roy, S.; Stern, D.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 473, Issue 2, p.2304-2323
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1
2018
Citations
20
Refereed citations
19
Description
AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star
(NS) low-mass X-ray binary showcasing intense ionized Fe K absorption.
We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data
sets (obtained between 2013 and 2016), therefore tripling the number of
observations of AX J1745.6-2901 in outburst. Thanks to simultaneous
XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the
X-ray continuum. During the soft state, the emission can be described by
a disc blackbody (kT ∼ 1.1-1.2 keV and inner disc radius
rDBB ∼ 14 km), plus hot (kT ∼ 2.2-3.0 keV) blackbody
radiation with a small emitting radius (rBB ∼ 0.5 - 0.8
km) likely associated with the boundary layer or NS surface, plus a
faint Comptonization component. Imprinted on the spectra are clear
absorption features created by both neutral and ionized matter.
Additionally, positive residuals suggestive of an emission Fe K α
disc line and consistent with relativistic ionized reflection are
present during the soft state, while such residuals are not significant
during the hard state. The hard-state spectra are characterized by a
hard (Γ ∼ 1.9-2.1) power law, showing no evidence for a high
energy cut-off (kTe > 60-140 keV) and implying a small
optical depth (τ < 1.6). The new observations confirm the
previously witnessed trend of exhibiting strong Fe K absorption in the
soft state that significantly weakens during the hard state. Optical
(GROND) and radio (GMRT) observations suggest for AX J1745.6-2901 a
standard broad-band spectral energy distribution as typically observed
in accreting NSs.
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